Mass transport of sucrose

Question 1

What does the phloem do?

Answer 1

= transports organic substances to all cells in a plant via the phloem

Question 2

What key features does the phloem contain?

Answer 2

= sieve tube elements
= companion cells
=

Question 3

What are the sieve tube elements?

Answer 3

= living cells
= contains ni nucleus
= contains few organelles
= holes in end, continious flow of sugar solution
= allows a hollow tuve

Question 4

What kind of transport is translocation?

Answer 4

= active transport, from low to high concentration gradient
= acrive process

Question 5

What features do companion cells have?

Answer 5

= provides ATP for active transport
= for transpirt of organic substances- sucrose

Question 6

What is the mass flow hypothesis?

Answer 6

= SOURCE: where the organic substance is produced, sucrose, created in leaves during phtosyntehsis
= SINK: where sucrose is transpored to and used, used by the respiring cells,

Question 7

Where is the phloem?

Answer 7

= next to the xylem transporting water

Question 8

What is the first step?

Answer 8

= sucrose lowers water potential of the source cell
= water enters the cell by osmosis- from surrounding cells
= at the sink cell, this is respricing, so using up the sucrose, so higher water potential, water leaves the sink cell by osmosis to the surrounding cells
= `

Question 9

What happens to the hydrostatic pressure?

Answer 9

= source cell has a higher hydrostatic pressure, more fluid is moving into it
= the sink cell will have a decrease hydrostatic pressure as liquid/water is moving out
= this forces the sugary solution out of the source cell and toewards the sink cell- moves on mass, pressure gradient to respiring cells by the phloem

Question 10

What happens at the source cell?

Answer 10

= photosynthesis occurs in chloroplast, creating organic substances e.g sucrose
=this creates a high concentration of sucrose at the source, sucrose diffuses down its concentration gradient into the companion cell by facilitated diffusion
= sucrose is activley transporte into the phloem/sieve tube elements, by co-transpirt withb h= ions

Question 11

What happens to the sucrose in the sieve tube element?

Answer 11

= increase of sucrose in the sive tube elements, reduces the water potential, xylem is directly next to the phloem, water moves into the sieve tube elements by osmosis,
= increase in water volume, in the sieve tube element increases the hydrostatic pressure causing the liquid to to be forced towards the sink, to a region of lower hydrosttaic pressure

Question 12

What happens with the transport of sucrose into the the sink? respiring cells

Answer 12

= sucrose is used in respiration, or stored as insoluable starch
= more sucrose is activley transported, into the sink cell, which causes the water potential to decrease, this results to osmosis to move into the sink cell, and some may flow back into the xylem
= the removal of water means there is a lower volume, the hydrostatic pressure is lower

Question 13

What is the first investigation for the phloem in which the organic substances are transpored through?

Answer 13

= plants provided with radioactiveley labelled co2
= this is absorbed during photosynthesis to produce sugars that are also radioactivley labelled
= samples were cut and placed on xray film detectes radioative material
= section containingin gth radioacitbe sihars were detected high;igjtog where phleo ws located

Question 14

What is the ringing experiment?

Answer 14

= ring of bark aling with the phloem are removed from the tree trunk
= trunk swells aboveremoevd ring, loquid was found to contain sugar
= sjowed that the phleom transports sugar as they cannot be transpryed die to the removal of the phloem